ИСТИНА

Picophytoplankton (cell size < 3 μm) play an important role in Arctic marine ecosystems. Changes in the pelagic marine environment in the Arctic Region are predicted to lead to increase of role of picoforms in the formation of the phytoplankton primary production and to increase the contribution of these smallest photoautotrophs in the total biomass of plankton algae [1]. In the same time the knowledge of picoalgae diversity and ecosystem functioning is limited especially in hard-to-reach areas. The Novaya Zemlya archipelago is located on the border of the Kara and Barents seas. Blagopoluchia Bay is the fjord-shaped bay of the Kara Sea on the eastern shore of the northern island of archipelago. The abundance and biomass of picophytoplankton, the total concentration of chlorophyll a (Chl), and the contribution of the picofraction to chlorophyll a (Chlpico), primary production (PPpico) and composition of picoalgae were studied in the Blagopoluchia Bay in September 2017. In the bay the upper euphotic zone varied from 6 to 17 m. Picophytoplankton was represented exclusively by phototrophic picoeukaryotes (PPEs). The PPEs abundance and biomass in euphotic zone varied from 0.36 to 0.55×109 cell/m3 and from 0.32 to 1.17 mg С/m3, respectively. The PPEs biomass increase from the top of the bay to the open sea. The average concentration of Chlpico in the upper euphotic zone was in the range of 0.01 to 0.17 mg/m3. The PPEs contribution to Chl averaged 18%. In the upper euphotic zone, PPpico was 1.6 mg C/m3 day-1, its contribution comprised 24% to total 14C primary productivity. High-throughput tag sequencing (Illumina MiSeq system) of the V4 region of the 18S rRNA gene was used to reveal the diversity of PPEs of the bay. A total of 396507 amplicons were sequenced, 150341 reads remained after quality filtering and preprocessing, and ~10% of quality sequences refers to PPEs. Subsequent to the clustering (97% similarity level) 221 OTUs of PPEs were generated. The identified OTUs belonged to seven classes of PPEs: Mamiellophyceae, Pyramimonadophyceae, Nephrophyceae, Treboxiophyceae, Mediophyceae, Bolidophyceae, and Coccolithophyceae. Mamiellophyceae dominated – 58% of all PPEs reads, Micromonas commoda, M. polaris, Bathycoccus prasinos, Mantoniella squamata and Mamiella gilva were revealed. The contribution of Mediophyceae and Coccolithophyceae reached 19% and 18% respectively. Diatoms Minidiscus trioculatus, Skeletonema marinoi, Chaetoceros cf. socialis and haptophyte Phaeocystis pouchetii, Chrysochromulina andersonii and Ch. leadbeateri were identified to the species level. The remaining OTUs (~5% of all PPEs reads) refer to bolidophyte Triparma strigata, chlorophyta Nephroselmis pyriformis and unidentified Pyramimonas sp., Crustomastix sp. and Chaetoceros sp.